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Abstract:

An object of the present invention is to provide a process for producing
high-purity hydroxytriphenylenes in which not only inexpensive raw
materials can be used but also no complicated steps of deprotection such
as dealkylation, and reduction and the like are necessary, and which is
thereby advantageous in industrial production. Also there is provided a
novel crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate, which
has satisfactory thermal stability. The process for producing a compound
represented by the general formula (2) is characterized by reacting a
compound represented by the general formula (1) in the presence of a
metal oxide comprising a metal selected from trivalent iron, pentavalent
vanadium and hexavalent molybdenum and of a nonvolatile strong acid:
##STR00001##
wherein, Rs are each independently a hydrogen atom, a halogen atom, an
alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3
carbon atoms.

Claims:

1-12. (canceled)

13. A crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate
obtained by reacting catechol in the presence of a metal oxide comprising
a metal selected from trivalent iron, pentavalent vanadium and hexavalent
molybdenum and of a nonvolatile strong acid, dissolving the resultant
2,3,6,7,10,11-hexahydroxytriphenylene in a mixed solvent of acetone and
water, and then adding a water to a obtained solution at a temperature in
a range from 5 to 50.degree. C.

14. A crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate
having, in a X-ray diffraction spectrum for CuKα characteristic
X-ray (wavelength: 1.5418 Å), main peaks at 9.3, 10.2 and 26.4 in
Bragg angle (2.theta..+-.0.2.degree.) thereof, and not having any peak
between 10.5 and 12.5.

15. The crystal according to claim 14, wherein a thermal decomposition
temperature (Td) is 140.degree. C.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a process for producing
hydroxytriphenylenes which are useful as a raw material for functional
materials such as, for example, discotic liquid crystal, in more detail,
the present invention relates to a process for producing
hydroxytriphenylenes in which 1,2-dihydroxybenzenes (hereinafter, may be
referred to simply as catechols) is used as a raw material, and a crystal
obtained by the process, as well as a novel crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate.

BACKGROUND OF THE INVENTION

[0002] Discotic liquid crystal has generally a disc-like central mother
nucleus and side chains extending radially from the mother nucleus
thereof, and recently various studies have been done in the liquid
crystal field due to anomalous liquid crystal property coming from its
structure. Examples of a compound to be the central mother nucleus of the
discotic liquid crystal are exemplified by, for example, benzene
derivatives, truxene derivatives, phthalocyanine derivatives,
triphenylene derivatives, cyclohexane derivatives, porphyrin derivatives,
and the like, and among them, triphenylene derivatives are the compounds
which attract attention in recent year because they tend to form a
discotic nematic phase, which is effective to form an optical functional
device.

[0003] Among these triphenylene derivatives, particularly various
production processes for 2,3,6,7,10,11-hexahydroxytriphenylene have been
reported since before, because suitable side chains can be easily
introduced at the positions of six hydroxyl groups and the other reason
etc.

[0004] Specifically, processes for producing a desired
2,3,6,7,10,11-hexahydroxytriphenylene have been known, by synthesizing
firstly chemically stable 2,3,6,7,10,11-hexaalkoxytriphenylene with using
1,2-dialkoxybenzene as a raw material (see, JP-A-7-330650, Synthesis,
477, 1994, etc.), then dealkylating with boron tribromide, hydrogen
iodide, and the like (see, JP-A-8-119894, J. Mater. Chem., 1992, 2, 1261,
etc.). However, since these processes not only required two steps of
trimerization step and dealkylation step, but also had such problems that
1,2-dialkoxybenzene as a raw material was comparatively expensive, and
boron tribromide and hydrogen iodide to be used in the dealkylation step
were highly corrosive, and the like, these processes were not suitable as
an industrial process for producing
2,3,6,7,10,11-hexahydroxytriphenylene.

[0005] As a method to solve such problems, a process for producing
directly 2,3,6,7,10,11-hexahydroxytriphenylene with using
1,2-dihydroxybenzene as a raw material has been attempted (see,
JP-A-9-118642, Synthesis, 477, 1994, etc.). Specifically, in Synthesis,
477, 1994, an iron complex of 2,3,6,7,10,11-hexahydroxytriphenylene has
been obtained by reacting catechol in the presence of anhydrous ferric
(III) chloride and 9.5-fold moles or more of sulfuric acid. However, it
has not been described that 2,3,6,7,10,11-hexahydroxytriphenylene has
been isolated from the iron complex. In addition, in JP-A-9-118642,
desired 2,3,6,7,10,11-hexahydroxytriphenylene has been obtained by
reacting catechol in the presence of ferric (III) chloride hydrate to
obtain an iron complex and/or a quinone derivative of
2,3,6,7,10,11-hexahydroxytriphenylene, which been then subjected to
reduction treatment. Thus, in these processes, although the problems of
productivity and corrosion can be solved because dealkylation step is not
required by using catechol as a raw material, the problem of requiring
many steps has not been solved because a reduction step is necessary to
obtain high-purity 2,3,6,7,10,11-hexahydroxytriphenylene in addition to a
trimerization step of catechol. Thus, these processes were not
advantageous one as an industrial production process.

[0006] Under such circumstance, a development of a production process for
synthesizing a high-purity 2,3,6,7,10,11-hexahydroxytriphenylene has been
demanded, in which not only inexpensive raw materials can be used but
also complicated steps of deprotection such as dealkylation from alkoxy
groups in hexaalkoxytriphenylene, and reduction of an iron complex and/or
a quinone derivative of hexahydroxytriphenylene are not necessary, and
which is thereby more easy and simple.

[0007] In addition, recently, as a technology relating to a crystal form
of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate, type A crystal of
the monohydrate has been disclosed in WO2005/090275. It has been
described that the type A crystal can be obtained by distilling off
acetone from a solution of 2,3,6,7,10,11-hexahydroxytriphenylene in mixed
solvent of acetone--water under a reduced pressure and a specified
temperature condition, and that the crystal form is superior in thermal
stability with a thermal decomposition temperature (Td) at about
139° C. In addition, in the WO2005/090275, it has been described
that all crystals (type B crystal in WO2005/090275) of
2,3,6,7,10,11-hexahydroxytriphenylene obtained by the well-known
production process in the prior art are poor in thermal stability, and
that an equipment built-in with the type B crystal is poor in durability
and has a disadvantage that it cannot exhibit a desired performance over
a long period of time. As obvious from this, the type B crystal obtained
by the existing production process did not have satisfactory performance.

[0008] Under such circumstance, an improvement from type B crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate having a poor thermal
stability to the one having a thermal stability comparable to at least
that of type A crystal of the monohydrate, that is,
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate having a superior
thermal stability as well as an establishment of a production process for
the compound has been demanded.

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

[0009] The present invention has been made considering the aforementioned
circumstances, and is directed to provide a process for producing
high-purity hydroxytriphenylenes in which not only inexpensive raw
materials can be used but also complicated steps of deprotection such as
dealkylation, and reduction and the like are not necessary, and which is
thereby advantageous in industrial production, and further a process for
producing a crystal of the hydroxyltriphenylenes.

[0010] In addition, the present invention is directed to provide novel two
types of crystals (hereinafter, may be referred to as type B' crystal and
type C crystal) of 2,3,6,7,10,1 1-hexahydroxytriphenylene monohydrate
having a superior thermal stability, which can be obtained by the
aforementioned production process.

Means to Solving the Problem

[0011] The present invention is an invention of a process for producing a
compound represented by the general formula (2) which comprises reacting
a compound represented by the general formula (1) in the presence of a
metal oxide comprising a metal selected from trivalent iron, pentavalent
vanadium and hexavalent molybdenum, and of a nonvolatile strong acid:

##STR00002##

wherein, two Rs are each independently a hydrogen atom, a halogen atom,
an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to
3 carbon atoms,

##STR00003##

wherein, six Rs are same as mentioned above.

[0012] In addition, the present invention is an invention of a crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate obtained by reacting
catechol in the presence of a metal oxide comprising a metal selected
from trivalent iron, pentavalent vanadium and hexavalent molybdenum and
of a nonvolatile strong acid, dissolving the resultant
2,3,6,7,10,11-hexahydroxytriphenylene in a mixed solvent of acetone and
water, and then distilling off acetone from a obtained solution at a
temperature in a range from 56 to 95° C.

[0013] Further, the present invention is an invention of a crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate obtained by reacting
catechol in the presence of a metal oxide comprising a metal selected
from trivalent iron, pentavalent vanadium and hexavalent molybdenum and
of a nonvolatile strong acid, dissolving the resultant
2,3,6,7,10,11-hexahydroxytriphenylene in a mixed solvent of acetone and
water, and then adding water to a obtained solution at a temperature in a
range from 5 to 50° C.

[0014] Furthermore, the present invention is an invention of a crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate having, in a X-ray
diffraction spectrum for CuKα characteristic X-ray (wavelength:
1.5418 Å), main peaks at 9.3, 10.2 and 26.4 in Bragg angle
(2θ±0.2°) thereof, and not having any peak between 10.5
and 12.5.

Effect of the Invention

[0015] According to the production process of the present invention, the
process not only has high productivity because a compound represented by
the general formula (1) (catechols) is used as a raw material, but also
can be synthesized in one step requiring no complicated step of
deprotection such as dealkylation, and reduction, and the like, and
further has less environmental load because oxidizing agent such as
organic peroxides is not used. Thus, high-purity
2,3,6,7,10,11-hexahydroxytriphenylenes can be produced more easily and
more simply.

[0016] In addition, since two types of crystals of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate of the present
invention obtained by recrystallizing
2,3,6,7,10,11-hexahydroxytriphenylene produced by the above process with
using catechol as a raw material under a specified condition, that is,
type B' crystal and type C crystal, have more superior thermal stability
in comparison with type B crystal obtained by the existing process, an
equipment built-in with the crystal of the present invention as a raw
material of a functional material has a superior stability (resistance to
denaturalization) and can exhibit a desired performance over a long
period of time.

[0022] The halogen atom represented by R in the general formulae (1) and
(2) includes a fluorine atom, a chlorine atom, a bromine atom, an iodine
atom, and the like. Among them, a fluorine atom, a chlorine atom and a
bromine atom are preferable, and a chlorine atom and a bromine atom are
more preferable.

[0023] The alkyl group having 1 to 3 carbon atoms represented by R in the
general formulae (1) and (2) may be any type of straight-chained or
branched, and specifically includes, for example, a methyl group, an
ethyl group, a n-propyl group, an isopropyl group, and the like. Among
them, a methyl group and an ethyl group are preferable, and a methyl
group is more preferable.

[0024] The alkoxy group having 1 to 3 carbon atoms represented by R in the
general formulae (1) and (2) may be any type of straight-chained or
branched, and specifically includes, for example, a methoxy group, an
ethoxy group, a n-propoxy group, an isopropoxy group, and the like. Among
them, a methoxy group and an ethoxy group are preferable, and a methoxy
group is more preferable.

[0025] As R in the general formulae (1) and (2), a hydrogen atom is more
preferable.

[0026] In the production process of the present invention, the compound
represented by the general formula (2) can be synthesized by trimerizing
the compound represented by the general formula (1) in water and/or a
polar solvent, in the presence of a specified amount of a metal oxide
comprising a metal selected from trivalent iron, pentavalent vanadium and
hexavalent molybdenum, relative to the compound represented by the
general formula (1), and of a nonvolatile strong acid. Further, two types
of crystals of monohydrate of the compound represented by the general
formula (2) can be selectively produced by selecting post-treatment
procedures mentioned later, so-called isolation and purification
procedures for the reaction solution after the trimerization reaction. In
addition, both of the two types of crystals (type B' crystal and type C
crystal) of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate, which can
be selectively produced by selecting catechol as the compound represented
by the general formula (1) and selecting isolation and purification
procedures mentioned later for the reaction solution after the
aforementioned trimerization reaction, have superior thermal stability.

[0027] As the compound represented by the general formula (1) to be used
in the present invention, that is, catechols, commercially available one
or the one synthesized by a common procedure may be used as appropriate.
In the present invention, as the compound represented by the general
formula (1), in particular, catechol, in which two Rs in the general
formula (1) are both hydrogen atoms, can be preferably used. In addition,
the compound represented by the general formula (2) to be synthesized by
using the catechol is 2,3,6,7,10,11-hexahydroxytriphenylene in which six
Rs in the general formula (2) are all hydrogen atoms. Namely, the present
invention is a particularly preferable production process as a process
for synthesizing high-purity 2,3,6,7,10,11-hexahydroxytriphenylene, which
is useful as a raw material of functional materials, with using
inexpensive catechol as a raw material.

[0028] The metal oxide comprising a metal selected from trivalent iron,
pentavalent vanadium and hexavalent molybdenum in the present invention
is not especially limited, so long as the metal oxide contains trivalent
iron, pentavalent vanadium or hexavalent molybdenum in its structure, and
is an oxide of these metals having oxidizing property. Specifically, the
metal oxide includes, for example, diiron trioxide (ferric oxide),
triiron tetroxide, divanadium pentoxide, molybdenum trioxide, and the
like, and among them, diiron trioxide (ferric oxide) is preferable. These
metal oxides may be used alone or in a combination of two or more kinds.
An amount of the metal oxide to be used is generally 1.0 to 10
equivalents, preferably 1.6 to 4 equivalents, as molar equivalent of
trivalent iron, pentavalent vanadium or hexavalent molybdenum, relative
to number of moles of the compound represented by the general formula
(1). The metal oxides less than 1.0 equivalent will lead to decrease in
yield of the desired compound represented by the general formula (2). On
the other hand, these metal oxides in an amount exceeding 10 equivalents
can be used, but result in such problems that economical efficiency is
lost, and the like.

[0029] Thus, in the present invention, it has been found that the desired
compound represented by the general formula (2) can be synthesized in
high yield and in high purity by using a metal oxide comprising a metal
selected from trivalent iron, pentavalent vanadium and hexavalent
molybdenum. Further, it has been found that a crystal of monohydrate of
the compound represented by the general formula (2) having a superior
thermal stability can be produced by combining the aforementioned
production process and the post-treatment procedures (isolation and
purification procedures) to be mentioned later.

[0030] In addition, the nonvolatile strong acid in the present invention
is not especially limited, so long as it is a nonvolatile strong acid
which can dissolve the aforementioned metal oxide comprising a metal
selected from trivalent iron, pentavalent vanadium and hexavalent
molybdenum, and does not bring about variation in concentration during
the reaction. Specifically, the nonvolatile strong acid includes, for
example, inorganic acids such as sulfuric acid, nitric acid, phosphoric
acid, and among them, sulfuric acid is preferable. These nonvolatile
strong acids may be used alone or in a combination of two or more kinds,
however, it is necessary to select a combination of nonvolatile strong
acids each of which does not adversely affect on the compound represented
by the general formula (1) as a raw material and the desired compound
represented by the general formula (2). In addition, an amount of the
nonvolatile strong acid to be used is not especially limited, so long as
it is an amount sufficient to dissolve the metal oxide comprising a metal
selected from trivalent iron, pentavalent vanadium and hexavalent
molybdenum or more. Specifically, molar equivalent value of hydrogen ion
in the nonvolatile strong acid, relative to number of moles of trivalent
iron, pentavalent vanadium and hexavalent molybdenum in the metal oxide
comprising a metal selected from trivalent iron, pentavalent vanadium and
hexavalent molybdenum is generally 5 to 60 equivalents, and preferably 6
to 40 equivalents.

[0031] As the reaction solvent, as mentioned above briefly, water and/or a
polar solvent can be used. The polar solvent cited here means a polar
solvent, which can dissolve the compound represented by the general
formula (1) as a raw material, and any polar solvent can be used so long
as it does not show reduction action. Specifically, the polar solvent
includes, for example, aprotic polar solvents such as acetonitrile,
acetone, dimethylformamide, dimethylsulfoxide, and the like, and among
them, dimethylformamide and dimethylsulfoxide are preferable. These
reaction solvents may be used alone or in a combination of two or more
kinds, and among them, preferably water is used alone. In addition, an
amount of these reaction solvents to be used is an amount sufficient to
dissolve the compound represented by the general formula (1) as a raw
material or more, and may be set as appropriate so that a value of
concentration in percent by weight of the nonvolatile strong acid in the
reaction system becomes a proper concentration. Specifically, for
example, molar equivalent of water and/or a polar solvent, relative to
number of moles of the compound represented by the general formula (1) is
generally 6 to 120 equivalents, and preferably 10 to 60 equivalents.

[0032] In the present invention, since reaction time and yield of the
desired compound represented by the general formula (2) vary depending on
a value of percent by weight of the nonvolatile strong acid in the
reaction system, it is desirable that the reaction is conducted in a
proper concentration. A proper value of the concentration in percent by
weight of the nonvolatile strong acid in the reaction system varies
depending on type of the nonvolatile strong acid and an amount thereof to
be used, type of the reaction solvent and an amount thereof to be used,
and the like, and it is difficult to determine unambiguously.
Specifically, a concentration in percent by weight of the nonvolatile
strong acid in the reaction system is in a range of generally 50 to 95%,
preferably 60 to 90%, and more preferably 70 to 85%. Among them, when the
nonvolatile strong acid is sulfuric acid, a concentration in percent by
weight is in a range of preferably 60 to 90% and more preferably 70 to
85%. In particular, when the reaction is carried out in a range of 70 to
85%, the desired compound represented by the general formula (2) can be
synthesized in a short time in a high yield hardly causing decomposition
of the desired compound represented by the general formula (2) and the
like. Also, as the nonvolatile strong acid, a commercially available one
in the aforementioned range of concentration in percent by weight may be
used as it is, or a diluted one may be used as appropriate.

[0033] Reaction temperature is desirably selected so that the compound
represented by the general formula (1) can be efficiently trimerized, and
specifically it is set in a range generally from 0 to 50° C.,
preferably from 20 to 45° C., and more preferably from 25 to
40° C. In particular, when the temperature is set in a range from
25 to 40° C., the desired compound represented by the general
formula (2) can be synthesized in a short time in a high yield hardly
causing decomposition of the desired compound represented by the general
formula (2) and the like.

[0034] In the production process of the present invention, the reaction
proceeds under any condition of normal pressure, pressurized and reduced
pressure, but preferably the reaction is conducted under normal pressure
where special facility is not needed.

[0035] Since reaction time may vary depending on molar equivalent number
of trivalent iron, pentavalent vanadium and hexavalent molybdenum in the
metal oxide comprising a metal selected from trivalent iron, pentavalent
vanadium and hexavalent molybdenum, relative to the compound represented
by the general formula (1), type of nonvolatile strong acid and an amount
thereof to be used, type of reaction solvent and an amount thereof to be
used, concentration in percent by weight of nonvolatile strong acid in
the reaction system, reaction temperature, and the like, the reaction
time cannot be determined unambiguously, but it is set in a range of
generally 0.5 to 20 hours, and preferably 2 to 12 hours.

[0036] In the present invention, as a process for purifying the desired
compound represented by the general formula (2) from the reaction
solution after completion of the reaction, not only crystal can be
purified but also two types of crystals can be selectively produced by
employing the procedure described below. Specifically, two types of
different crystals can be selectively produced by (a) dissolving the
compound represented by the general formula (2) obtained by the
production process of the present invention in a mixed solvent of acetone
and water, and distilling off acetone from a obtained solution at a
temperature in an appropriate range to precipitate crystal of the
compound represented by the general formula (2), or by (b) dissolving the
compound represented by the general formula (2) obtained by the
production process of the present invention in a mixed solvent of acetone
and water, and adding a water to a obtained solution at a temperature in
an appropriate range to precipitate crystal of the compound represented
by the general formula (2). Namely, two different types of crystals
having superior thermal stability can be selectively produced by
combining the production process of the present invention and further one
of the crystal precipitation processes described above. In addition, the
compound represented by the general formula (2) obtained by the
production process of the present invention to be used for obtaining the
desired crystal by a specific procedures as cited here, may be the one
which is taken out by the common procedure from the reaction solution
after completion of the reaction by the production process of the present
invention, or the one of crude crystal. More specifically, for example,
since crude crystal can be obtained by pouring the reaction solution
after completion of the reaction into water, or pouring the water into
the reaction solution and collecting the resultant precipitate by
filtration, this crude crystal may be used. Alternatively, the crystal
obtained by further washing the crude crystal with water and the like may
be used, or the crystal further purified by column chromatography or the
like may be used.

[0037] More specific crystal precipitation procedure of the aforementioned
method (a) is as follows. For example, when the compound represented by
the general formula (2) obtained by the production process of the present
invention is crude crystal obtained by the aforementioned process, the
crude crystal is dispersed in acetone, after that the dispersion liquid
is stirred at room temperature, and filtered to filter off insoluble
matter. Furthermore, activated charcoal is added to the filtrate, and the
liquid is then stirred at room temperature, followed by filtering off the
activated charcoal. To the filtrate obtained by such treatment, a
specified amount of water is added to make a solution containing a mixed
solvent of acetone and water, from which acetone is distilled off under
normal pressure at a temperature in an appropriate range to precipitate a
crystal. The crystal is collected by filtration and dried. The crystal
can be precipitated (crystallized) in such way. Also, when
crystallization is carried out using the crystal, which purified further
the aforementioned crude crystal by column chromatography or the like,
the dispersion treatment with acetone and the activated charcoal
treatment are not necessarily carried out.

[0038] An amount of acetone to be used in the mixed solvent of acetone and
water may be an amount sufficient to dissolve whole amount of the
compound represented by the general formula (2). More specifically, an
amount of acetone is, for example, generally around 2 mL or more,
preferably around 3 to 100 mL, and more preferably around 5 to 60 mL per
1 g of the compound represented by the general formula (2) obtained by
the production process of the present invention, which is a target of
crystallization. When an excess amount of acetone is used, for example,
in the aforementioned activated charcoal treatment, an amount of acetone
to be used is desirably set in the aforementioned range by distilling off
acetone before adding the water into the filtrate after the activated
charcoal treatment.

[0039] An amount of water to be used in the mixed solvent of acetone and
water may be an amount of such level that the compound represented by the
general formula (2) dissolved in acetone does not precipitate in the
water addition stage, but the crystal precipitates with distilling off
acetone from the solution containing the mixed solvent of acetone and
water. More specifically, a mixing ratio of water is, for example,
generally around 10 to 500 mL, preferably around 30 to 300 mL, and more
preferably around 50 to 200 mL per 100 mL of acetone in the mixed solvent
of acetone and water. When water is added to the filtrate, for example,
after the aforementioned activated charcoal treatment, an amount of water
to be added is desirably adjusted so that the mixing ratio of acetone and
water falls in the aforementioned range.

[0040] In the method (a) of the present invention, acetone is distilled
off in obtaining the crystal, and this distilling off is carried out
under normal pressure. Therefore, temperature when acetone is distilled
off from the solution containing the mixed solvent of acetone and water
is set at generally 56° C. or higher, and preferably at a
temperature in a range from 56 to 95° C. In the precipitation
method (a), the crystal having the desired crystal form is desirably
crystallized at 70° C. or higher. In addition, since the compound
represented by the general formula (2) has a property that it is soluble
in acetone but insoluble in water, in order to precipitate crystal by
distilling off acetone from the solution containing the mixed solvent,
distilling off of acetone starts at 56° C., which is a boiling
point of acetone under normal pressure, or higher, and crystallization is
performed at 70° C. or higher and practically completed within a
temperature range from 70 to 80° C. Also, when crystallization can
be done at 70° C. or higher, acetone may be distilled off
generally at 70° C. or higher, and preferably at a temperature in
a range from 70 to 80° C.

[0041] As mentioned above briefly, the crystal precipitated in such way
may be isolated by a common procedure. Specifically, the crystal having
the desired crystal form can be obtained, for example, by collecting the
crystal by a filtration means such as suction filtration, followed by
drying the obtained crystal under reduced pressure.

[0042] On the other hand, more specific crystal precipitation procedure
(purifying method) of the aforementioned method (b) is as follows. For
example, when the compound represented by the general formula (2)
obtained by the production process of the present invention is crude
crystal obtained by the aforementioned process, the crude crystal is
dispersed in acetone, after that the dispersion liquid is stirred at room
temperature, and filtered to filter off insoluble matter. Furthermore,
activated charcoal is added to the filtrate, and the liquid is then
stirred at room temperature, followed by filtering off the activated
charcoal. The filtrate obtained by such treatment is once evaporated to
dryness by condensing and distilling off acetone under reduced pressure,
and then specified amounts of acetone and water are added to the
resultant residue. A crystal is precipitated by adding the water to the
obtained solution containing the mixed solvent of acetone and water at a
temperature in an appropriate range, collected by filtration, and then
dried. The crystal can be precipitated (crystallized) in such way. Also,
when crystallization is carried out using the crystal which purified
further the aforementioned crude crystal by column chromatography or the
like, the dispersion treatment with acetone and the activated charcoal
treatment are not necessarily carried out.

[0043] An amount of acetone to be used in the mixed solvent of acetone and
water may be an amount sufficient to dissolve whole amount of the
compound represented by the general formula (2). More specifically, an
amount of acetone is, for example, generally around 1 to 30 mL,
preferably around 1.5 to 20 mL, and more preferably around 2 to 10 mL per
1 g of the compound represented by the general formula (2) obtained by
the production process of the present invention, which is a target of
crystallization. In order to precipitate crystal efficiently, the
compound represented by the general formula (2) is dissolved desirably
using as small amount as possible of acetone.

[0044] An amount of water to be used in the mixed solvent of acetone and
water may be an amount of such level that the compound represented by the
general formula (2) dissolved in acetone does not precipitate. More
specifically, a mixing ratio of water is, for example, generally around 5
to 100 mL, preferably around 10 to 90 mL, and more preferably around 20
to 80 mL per 100 mL of acetone in the mixed solvent of acetone and water.
Thus, the compound represented by the general formula (2) can be
effectively dissolved by using the mixed solvent of acetone and water by
adding an appropriate amount of water to acetone.

[0045] An amount of water to be added to the solution containing the mixed
solvent of acetone and water may be an amount of such level that the
compound represented by the general formula (2) dissolved in the mixed
solvent of acetone and water precipitates by the addition of water. More
specifically, an additional ratio of water is, for example, generally
around 200 to 2000 mL, preferably around 250 to 1500 mL, and more
preferably around 300 to 1200 mL per 100 mL of acetone in the mixed
solvent of acetone and water.

[0046] Temperature at which water is added to the solution containing the
mixed solvent of acetone and water should be set at a temperature at
which the crystal having the desired crystal form precipitates, and
specifically, set at a temperature in a range generally from 5 to
50° C., and preferably from 10 to 35° C. In the
precipitation method (b), since the crystal having the desired crystal
form is desirably crystallized at 50° C. or lower, in addition,
the compound represented by the general formula (2) has a property that
it is soluble in acetone but insoluble in water, in order to precipitate
crystal to precipitate by adding a water to the solution containing the
mixed solvent, crystallization is carried out while the solution kept at
50° C. is slowly cooled down to 5° C. and kept at this
temperature, in particular, crystallization is preferably completed
within a temperature range from 10 to 35° C.

[0047] As mentioned above briefly, the crystal precipitated in such way
may be isolated by a common procedure. Specifically, the crystal having
the desired crystal form can be obtained, for example, by collecting the
crystal by a filtration means such as suction filtration, followed by
drying the filtered crystal under reduced pressure.

[0048] As mentioned above, two types of crystals having the different
crystal forms can be produced by combining the production process of the
present invention and further the crystal precipitation procedure
(crystallization method). When a crude crystal is crystallized,
purification can be done simultaneously by this procedure.

[0049] Also, in the isolation and purification procedures, when a crystal
form of the compound represented by the general formula (2) to be
obtained need not to be considered, any one among the well-known
isolation and purification procedures can be employed. More specifically,
for example, reaction solution is poured into water, or water is poured
into reaction solution, the resultant precipitate is collected by
filtration, and then collected crude crystal is washed with water.
Thereafter, the crude crystal is dispersed in a mixed solvent of water
and a suitable polar solvent, and the dispersion liquid is heated up to a
specified temperature with stirring, then filtered in hot state at the
same temperature. The filtrate is concentrated and precipitated crystal
is collected by filtration. The crystal can be purified efficiently in
such way.

[0050] In the isolation and purification procedures, the polar solvent to
be used for dispersing the crude crystal includes, for example, an
aprotic polar solvent such as acetonitrile, acetone. In addition, in the
filtration in hot state, a filter aid such as diatom earth, activated
charcoal may be used in combination.

[0051] As mentioned above, in the production process of the present
invention, even when any of the isolation and purification procedures
described above is employed, any metal including iron and the like used
in the reaction can be removed. Further, according to the present
invention, since oxidizing agent such as organic peroxide is not used,
complicated steps such as reduction, liquid separation and extraction to
remove excess organic peroxide are not required as a post-treatment
procedure, and the desired compound represented by the general formula
(2) can be isolated and purified by easy and simple procedures.

[0052] In addition, in the production process of the present invention, a
crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate having
superior thermal stability can be produced by crystallizing
2,3,6,7,10,11-hexahydroxytriphenylene which is obtained by using catechol
as the compound represented by the general formula (1) employing any one
among the crystallization procedures of the method (a) and method (b)
described above. More specifically, when
2,3,6,7,10,11-hexahydroxytriphenylene obtained by the production process
of the present invention is crystallized according to the method (a),
type B' crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate can
be produced, and when 2,3,6,7,10,11-hexahydroxytriphenylene obtained by
the production process of the present invention is crystallized according
to the method (b), type C crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate can be produced.
Furthermore, the type B' crystal and the type C crystal of the
monohydrate obtained by the aforementioned method (a) and method (b),
respectively, are both superior in thermal stability.

[0053] Namely, the present inventors have found that type B' crystal and
type C crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate, both
having more superior thermal stability compared to that of type B crystal
of the monohydrate obtained by existing production process, can be
obtained by further crystallizing 2,3,6,7,10,11-hexahydroxytriphenylene
obtained by the production process of the present invention using a
specific crystallization method. More specifically, the present inventors
have disclosed for the first time that although the well-known type B
crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate is inferior
in thermal stability, the crystal of the monohydrate obtained by the
production process of the present invention further combined with a
specific crystallization method, that is, a specific recrystallization
method, is superior in thermal stability. In addition, the present
inventors have found, as a result of intensive studies, that the type C
crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate having
superior thermal stability is a novel one. As mentioned above, the
present invention has been completed based on such knowledge.

[0054] The type B' crystal of 2,3,6,7,10,11-hexahydroxytriphenylene
obtained according to the process (crystallization method) of the present
invention is composed of 2,3,6,7,10,11-hexahydroxytriphenylene
monohydrate, and it has been identified by Karl-Fischer method that the
type B' crystal is monohydrate.

[0055] In addition, the type B' crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate has main peaks at 11.4,
17.2, 22.6, 26.1 and 27.7 in Bragg angle (2θ±0.2°) in a
X-ray diffraction spectrum for CuKα characteristic X-ray
(wavelength: 1.5418 Å), and these data are similar to the X-ray data
of the type B crystal of 2,3,6,7,10,11-hexahydroxytriphenylene
monohydrate described, for example, in WO2005/090275. However, since the
type B' crystal according to the present invention is more superior in
thermal stability compared with the well-known type B crystal, and
further, the well-known type B crystal has a thermal decomposition
temperature (Td) at about 162° C. whereas the type B' crystal
according to the present invention has no thermal decomposition
temperature (Td), though details are not clear, it is suggested that the
type B' crystal according to the present invention is a compound which
has a structure based on the physical properties different from those of
the well-known type B crystal.

[0056] The type C crystal from 2,3,6,7,10,11-hexahydroxytriphenylene
obtained according to the process (crystallization method) of the present
invention is composed of 2,3,6,7,10,11-hexahydroxytriphenylene
monohydrate, and it has been identified by Karl-Fischer method that the
type C crystal is monohydrate.

[0057] In addition, the type C crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate has main peaks at 9.3,
10.2 and 26.4 in Bragg angle (2θ±0.2°) in a X-ray
diffraction spectrum for CuKα characteristic X-ray (wavelength:
1.5418 Å), and does not have any peak between 10.5 and 12.5 in Bragg
angle (2θ±0.2°) (this means in other words "any peak
cannot be clearly identified in this range"), and further, thermal
analysis (TG/DTA) of the type C crystal reveals that the type C crystal
is a novel crystal with a thermal decomposition temperature (Td) at
140° C., and more superior in thermal stability compared with the
well-known type B crystal.

[0058] Hereinafter, the present invention will be specifically explained
referring to Examples, but the present invention is not limited thereto
by any means.

EXAMPLES

Example 1

Synthesis of 2,3,6,7,10,11-hexahydroxytriphenylene Using Catechol as a
Starting Material and Diiron Trioxide (Ferric Oxide) as a Metal Oxide
Comprising a Trivalent Iron

[0059] Catechol (22.0 g, 0.2 moles) and diiron trioxide (ferric oxide)
(31.9 g, 0.2 moles) were added into water (110 mL), and 98% sulfuric acid
(440 g, 4.4 moles) was added dropwise to the solution while temperature
of the solution was maintained at 30° C. or lower, to adjust the
concentration in percent by weight of sulfuric acid in the reaction
system at 80%. The solution was reacted at 30° C. for 6 hours with
stirring. After completion of the reaction, water (500 mL) was added
dropwise to the reaction solution, and the reaction solution was stirred
for another 30 minutes. The resultant precipitate was collected by
filtration, and the obtained crude crystal was washed with water and
dried to give crude crystal (19.2 g). After a part of the crude crystal
(5.0 g among 19.2 g) was dispersed in a mixed solvent of water (50 mL)
and acetonitrile (200 mL), the dispersion liquid was heated up and
stirred for 1 hour. After that, this dispersion liquid was filtered in
hot state to filter off insoluble matter, the filtrate was then
concentrated under reduced pressure, and the precipitated crystal was
collected by filtration, and then dried, to give
2,3,6,7,10,11-hexahydroxytriphenylene (2.56 g, theoretical yield from
catechol: 45.5%) in black powder form. 1H-NMR data of the obtained
2,3,6,7,10,11-hexahydroxytriphenylene measured were in accordance with
those of 2,3,6,7,10,11-hexahydroxytriphenylene described in the
reference. Also, the measurement results of 1H-NMR are shown below.
In addition, content of iron ion in the obtained crystal was measured by
inductively-coupled plasma optical emission spectroscopy (ICP-OES), and
was found that content of iron ion (reduced quantity from metal iron) in
the obtained 2,3,6,7,10,11-hexahydroxytriphenylene (2.56 g) was 0.087 mg
(0.034 mg/g). Also, the measurement of iron ion content by
inductively-coupled plasma optical emission spectroscopy was carried out
using inductively-coupled plasma optical emission spectrometer SPS 3100
(manufactured by SII Nanotechnology Inc.) as follows. Several samples
containing appropriate amount of metal iron dissolved in
n-methyl-2-pyrrolidone were measured and a calibration curve was obtained
based on the measurement results, in advance. Content of iron ion in
2,3,6,7,10,11-hexahydroxytriphenylene was obtained from the calibration
curve.

[0060]1H-NMR (400 MHz, DMSO-d6) δ (ppm): 7.61 (s, Ar), 9.27
(s, OH).

Example 2

Synthesis of 2,3,6,7,10,11-hexahydroxytriphenylene Using Catechol as a
Starting Material and Divanadium Pentoxide (Vanadium (V) Oxide) as a
Metal Oxide Comprising Pentavalent Vanadium

[0061] Catechol (22.0 g, 0.2 moles) and divanadium pentoxide (vanadium (V)
oxide) (36.4 g, 0.2 moles) were added into water (110 mL), and 98%
sulfuric acid (440 g, 4.4 moles) was added dropwise to the solution while
temperature of the solution was maintained at 30° C. or lower, to
adjust the concentration in percent by weight of sulfuric acid in the
reaction system at 80%. The solution was reacted at 30° C. for 6
hours with stirring. After completion of the reaction, water (500 mL) was
added dropwise to the reaction solution while temperature of the solution
was maintained at 30° C. or lower, and the reaction solution was
stirred at the same temperature for another 30 minutes. The resultant
precipitate was collected by filtration, and the obtained crude crystal
was washed with water. The crude crystal was further dispersed in water
(1 L), and the dispersion liquid was stirred for 30 minutes, and then
filtered to collect crystal. After the collected crystal was dispersed in
acetone (400 mL), the dispersion liquid was stirred for 30 minutes. After
that, the dispersion liquid was filtered to filter off insoluble matter,
and the filtrate was concentrated under reduced pressure to distill off
an excess amount of acetone. Subsequently, water (160 mL) was poured into
the concentrated filtrate (solution of about 160 mL). This solution was
slowly heated up from 56° C. under normal pressure to concentrate
the solution. Crystal precipitated when temperature of the concentrated
solution became 70 to 80° C. Concentration was further continued,
and stopped when temperature of the concentrated solution became
90° C. The crystal thus precipitated was collected by filtration,
and then dried, to give 2,3,6,7,10,11-hexahydroxytriphenylene (7.27 g,
theoretical yield from catechol: 33.6%) in black powder form. Also, the
obtained compound in black powder form was identified to be
2,3,6,7,10,11-hexahydroxytriphenylene by measuring 1H-NMR in the
same way as in Example 1.

Example 3

Synthesis of 2,3,6,7,10,11-hexahydroxytriphenylene Using Catechol as a
Starting Material and Molybdenum Trioxide (Molybdenum (VI) Oxide) as a
Metal Oxide Comprising Hexavalent Molybdenum

[0062] Catechol (22.0 g, 0.2 moles) and molybdenum trioxide (molybdenum
(VI) oxide) (57.54 g, 0.4 moles) were added into water (110 mL), and 98%
sulfuric acid (440 g, 4.4 moles) was added dropwise to the solution while
temperature of the solution was maintained at 30° C. or lower, to
adjust the concentration in percent by weight of sulfuric acid in the
reaction system at 80%. The solution was reacted at 30° C. for 6
hours with stirring. Reaction rate after reacting for 6 hours was 18.0%.
Also, the reaction rate was determined by taking out a part of the
solution after reacting for 6 hours and measuring the solution by high
performance liquid chromatography (HPLC). In addition, the peak detected
by high performance liquid chromatography (HPLC) was confirmed to be
2,3,6,7,10,11-hexahydroxytriphenylene by the fact that it corresponded to
the peak of 2,3,6,7,10,11-hexahydroxytriphenylene obtained by the
existing process. Namely, the compound obtained in Example 3 was
identified to be 2,3,6,7,10,11-hexahydroxytriphenylene by the fact that
the retention time in HPLC of the compound obtained in Example 3 was in
accordance with the retention time in HPLC of
2,3,6,7,10,11-hexahydroxytriphenylene obtained by the existing process.
Also, identification by high performance liquid chromatography (HPLC) was
carried out under the following conditions: Intelligent HPLC Pump Model
PU-980 and Intelligent UV/VIS Detector Model UV-970 (manufactured by
JASCO Corp.), Column: Wakosil-II 5C-18, 4.6 mm×150 mm (Wako Pure
Chemical Industries, Ltd.), Eluent: Acetonitrile/Water/Phosphoric
Acid/Triethylamine=200 mL/800 mL/2 mL/2 mL, Measurement Wavelength: 275
nm. In addition, the aforementioned reaction rate was determined as
follows. Firstly, several samples containing appropriate amounts of
2,3,6,7,10,11-hexahydroxytriphenylene dissolved in the above eluent were
measured using the aforementioned HPLC instrument and the like to obtain
peak areas, and a calibration curve was obtained based on the peak areas,
in advance. The reaction rate was calculated by comparing the peak area
in HPLC measurement of the solution after reaction (an amount of the
solution after reaction taken out was converted to an amount of whole
solution after reaction) and that of the calibration curve, and by
determining an abundance of 2,3,6,7,10,11-hexahydroxytriphenylene in the
solution after reaction.

Example 4

Synthesis of Type B' Crystal of 2,3,6,7,10,11-hexahydroxytriphenylene
monohydrate Using Catechol as a Starting Material and Diiron Trioxide
(Ferric Oxide) as a Metal Oxide Comprising Trivalent Iron

[0063] Catechol (22.0 g, 0.2 moles) and diiron trioxide (ferric oxide)
(31.9 g, 0.2 moles) were added into water (44 mL), and 98% sulfuric acid
(176 g, 1.76 moles) was added dropwise to the solution while temperature
of the solution is maintained at 30° C. or lower, to adjust the
concentration in percent by weight of sulfuric acid in the reaction
system at 80%. The solution was reacted at 30° C. for 6 hours with
stirring. After completion of the reaction, water (200 mL) was added
dropwise to the reaction solution while temperature of the solution was
maintained at 30° C. or lower, and the reaction solution was
stirred at the same temperature for another 30 minutes. The resultant
precipitate was collected by filtration, and the obtained crude crystal
was washed with water. The crude crystal was further dispersed in water
(400 mL), and the dispersion liquid was stirred for 30 minutes, and then
filtered to collect crystal. After the collected crystal was dispersed in
acetone (400 mL), the dispersion liquid was stirred for 30 minutes. After
that, the dispersion liquid was filtered to filter off insoluble matter,
and activated charcoal (10.81 g) was added to the filtrate, which was
then stirred for 30 minutes. After stirring, the filtrate was
concentrated under reduced pressure to distill off an excess amount of
acetone. Subsequently, water (160 mL) was poured into the concentrated
filtrate (solution of about 160 mL). This solution was slowly heated up
from 56° C. under normal pressure to concentrate the solution.
Crystal precipitated when temperature of the concentrated solution became
70 to 80° C. Concentration was further continued, and stopped when
temperature of the concentrated solution became 90° C. The crystal
thus precipitated was collected by filtration, and then dried, to give
type B' crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate
(9.32 g, theoretical yield from catechol: 40.8%) in dark yellow powder
form. Also, water content of the obtained the type B' crystal was
measured using a Karl-Fischer measuring instrument (Moisture Meter
KF-200, manufactured by Mitsubishi Chem. Corp.), and found to be 5.5%. On
the other hand, since molecular weight of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate was 342.30
(C18H12O.sub.6.H2O) and that of water was 18.02, and also
theoretical water content of 2,3,6,7,10,11-hexahydroxytriphenylene
monohydrate was 5.26%, the obtained type B' crystal was confirmed to be
monohydrate of 2,3,6,7,10,11-hexahydroxytriphenylene.

Example 5

Synthesis of Type C Crystal of 2,3,6,7,10,11-hexahydroxytriphenylene
monohydrate Using Catechol as a Starting Material and Diiron Trioxide
(Ferric Oxide) as a Metal Oxide Comprising Trivalent Iron

[0064] Catechol (22.0 g, 0.2 moles) and diiron trioxide (ferric oxide)
(31.9 g, 0.2 moles) were added into water (44 mL), and 98% sulfuric acid
(176 g, 1.76 moles) was added dropwise to the solution while temperature
of the solution is maintained at 30° C. or lower, to adjust the
concentration in percent by weight of sulfuric acid in the reaction
system at 80%. The solution was reacted at 30° C. for 6 hours with
stirring. After completion of the reaction, water (200 mL) was added
dropwise to the reaction solution while temperature of the solution was
maintained at 30° C. or lower, and the reaction solution was
stirred at the same temperature for another 30 minutes. The resultant
precipitate was collected by filtration, and the obtained crude crystal
was washed with water. The crude crystal was further dispersed in water
(400 mL), and the dispersion liquid was stirred for 30 minutes, and then
filtered to collect crystal. After the collected crystal was dispersed in
acetone (400 mL), the dispersion liquid was stirred for 30 minutes. After
that, the dispersion liquid was filtered to filter off insoluble matter,
and activated charcoal (10.81 g) was added to the filtrate, which was
then stirred for 30 minutes. After stirring, the filtrate was
concentrated under reduced pressure to distill off acetone, and
evaporated to dryness. After the residue after evaporation to dryness was
dissolved by adding the acetone (40 mL) and the water (20 mL) thereto at
room temperature, water (380 mL) was slowly added dropwise at the same
temperature. By cooling down the solution after the addition to
10° C., crystal precipitated. The crystal thus precipitated was
collected by filtration, and then dried, to give type C crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate (8.43 g, theoretical
yield from catechol: 36.9%) in reddish purple powder form. Also, water
content of the obtained the type C crystal was measured by Karl-Fischer
method in the same way as in Example 4, and the type C crystal was
confirmed to be monohydrate of 2,3,6,7,10,11-hexahydroxytriphenylene.

[0065] Measurement of X-ray powder diffraction spectra of type B' and type
2 5 C crystals of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate
obtained was carried out using RINT 2000/PC (manufactured by Rigaku
Corp.), and Cu radiation having λ=1.5418 Å through a
monochromator, to obtain X-ray diffraction spectra. The measurement
results for the type B' crystal and for the type C crystal are shown in
FIG. 1 and FIG. 2, respectively, and also, values of main peaks in these
spectra are shown in Table 1 (peak data for the type B' crystal) and
Table 2 (peak data for the type C crystal), respectively.

[0066] Measurement of thermometric analyses (TG/DTA) of the type B' and
the type C crystals of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate
obtained was carried out using thermometric analyzer TAPS 3000S
manufactured by Bruker AXS Corp. under the following conditions:
measuring temperature range: 30 to 500° C., temperature rising
rate: 10° C./minute, carrier gas: argon gas (100 mL/minute). About
10 mg of the crystal to be analyzed was weighed on the aluminum-made
shallow dish, which was placed on a sample dish of the analyzer, and
subjected to the measurement under the aforementioned conditions. Also,
as a reference, about 10 mg of αAl2O3 was used. As the
results of the measurement, the type B' Crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate was found to have no
thermal decomposition temperature (Td), but the type C crystal was found
to have thermal decomposition temperature (Td) at 140° C. The
measurement results of thermometric analyses of the type B' crystal is
shown in FIG. 3, and the measurement results of thermometric analyses of
the type C crystal is shown in FIG. 4.

Comparative Example 1

Synthesis of Type B Crystal of 2,3,6,7,10,11-hexahydroxytriphenylene
monohydrate by an Existing Process

[0067] A type B crystal of 2,3,6,7,10,11-hexahydroxytriphenylene
monohydrate was synthesized according to the process described in
Synthesis, 477, 1994 and JP-A-8-119894. Namely, 1,2-dimethoxybenzene
(31.78 g, 0.23 moles) and anhydrous ferric chloride (120 g, 0.74 moles)
were dissolved in 70% sulfuric acid, and the solution was reacted at
25° C. for 24 hours with stirring. After completion of the
reaction, the solution was poured into ice water (500 g), and the
precipitated crystal was collected by filtration. After the resultant
crystal was washed with water (1 L), and then dried to give pale purple
colored 2,3,6,7,10,11-hexamethoxytriphenylene (28.2 g, theoretical yield
from 1,2-dimethoxybenzene: 90.1%) (the method of Synthesis, 477, 1994).

[0068] Subsequently, to the obtained 2,3,6,7,10,11-hexamethoxytriphenylene
(28.2 g, 0.069 moles), 57% hydroiodic acid (235.3 g, 1.05 moles) and
acetic acid (145 mL) were added, and the solution was refluxed for 2
hours. After completion of the reaction, the solution was cooled down to
room temperature, and the precipitated crystal was collected by
filtration. The crystal collected by filtration was dried under reduced
pressure to give gray type B crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate (20.2 g, yield: 85.5%)
(the method of JP-A-8-119894). Also, the resultant gray compound was
confirmed to be 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate by
1H-NMR analysis and measurement of water content by Karl-Fischer
measuring instrument. In addition, the measurement results of X-ray
powder diffraction spectrum of the type B crystal are shown in FIG. 5 and
also, main peak values of the type B crystal are shown in Table 3. Also,
the measurement of X-ray powder diffraction spectrum was carried out in
the same way as in Example 6.

[0069] Experimental Example 1: Thermal stability test for type B' crystal,
type C crystal and type B crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate obtained in Examples 4
and 5, and Comparative Example 1 Each of type B' crystal, type C crystal
and type B crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate
obtained in Examples 4 and 5, and Comparative Example 1 (50 mg each) was
dissolved in methanol and total volume of each solution was adjusted to
100 mL, to prepare methanol solution of each crystal. Visible-ultraviolet
spectroscopy was measured by filling a quartz cell with the methanol
solution and using methanol as a reference. Measurement by
visible-ultraviolet spectroscopy was carried out using
ultraviolet-visible spectrophotometer UV-2550 manufactured by Shimadzu
Corp. as a visible-ultraviolet spectrometry instrument and a quartz cell
having an optical path length of 10 mm, by measuring the absorbance at
360 nm and 520 nm.

[0070] In addition, each of quartz cells used in the measurement was left
to stand in a thermostatic chamber maintained at 60° C. for
predetermined days, and on the cells left stand for predetermined days,
absorbance at 360 nm and 520 nm was measured in the same way as described
above. The results are shown in Table 4.

[0071] From the results in Table 4, since the type B' crystal and the type
C crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate obtained
in Examples 4 and 5 show little difference even after leaving stand for
21 days at 60° C. in any of the values of absorbance at 360 nm and
520 nm, it can be understood that these crystals hardly change even at
60° C., and are superior in thermal stability. On the other hand,
since the type B crystal of the well-known
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate obtained in Comparative
Example 1 shows increases in both of the values of absorbance at 360 nm
and 520 nm by leaving stand at 60° C. for 21 days, and also in
visual observation, the methanol solutions shows significant
discoloration by the day, it can be understood that this type B crystal
is inferior in thermal stability causing some change at 60° C.
Also, as obvious from the measurement results of iron ion content in
Example 1, it is considered to be contributing to the thermal stability
of the monohydrate crystal that little amount of metal oxide of iron and
the like is contained in 2,3,6,7,10,11-hexahydroxytriphenylene obtained
by the production process of the present invention.

[0072] As mentioned above, from the results of Examples 1 to 3, it can be
understood that a high-purity desired compound represented by the general
formula (2) can be isolated and purified with easy and simple procedures
such as recrystallization in high yield by conducting the reaction in the
presence of a metal oxide comprising a metal selected from trivalent
iron, pentavalent vanadium and hexavalent molybdenum and of a nonvolatile
strong acid. When ferric (III) chloride is used as in the existing
process, a reduction step is required to reduce an iron complex and/or
quinone derivative of the compound represented by the general formula
(2). Whereas in the production process of the present invention in which
a metal oxide of a specified metal is used in the reaction, isolation and
purification can be done by easy and simple procedures such as a common
recrystallization without requiring any reduction step. Therefore, it is
considered that in the reaction, the iron complex and/or quinone
derivative of the compound represented by the general formula (2) are not
formed or formations thereof are significantly inhibited. Further, since
the production process of the present invention is the one in which most
of metals including the metal such as iron used in the reaction can be
efficiently removed by a easy and simple procedures such as a usual
recrystallization, as obvious from the measurement results of iron ion
content in Example 1, it is a superior process which does not require a
special step to remove metals (metal oxides) such as iron and the like.
In addition, the production process of the present invention has less
environmental load because combined use of oxidizing agent such as
organic peroxide is not needed, and does not require a complicated step
such as reduction, liquid separation, extraction. Therefore, the
production process of the present invention is an advantageous process
for production in an industrial scale.

[0073] Furthermore, from the results of Examples 4 to 7 and Experimental
Example 1, the crystal obtained by combining the production process of
the present invention and further the specified crystal precipitation
process (crystallization method) has a more superior thermal stability
compared with the well-known type B crystal. Namely, as obvious from the
results of Example 6 and Comparative Example 1, the type B' crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate obtained in Example 4
has a similar X-ray powder diffraction spectrum to that of the type B
crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate obtained in
Comparative Example 1. However, as obvious from the results of Example 7,
the type B' crystal does not have thermal decomposition temperature (Td)
which is possessed by the known type B crystal, and further, as obvious
from the results of Experimental Example 1, the type B' crystal has a
superior thermal stability differing from the well-known type B crystal.
Therefore, it is suggested that the type B' crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate according to the
present invention is a compound having a different structure from that of
the well-known type B crystal. On the other hand, the type C crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate according to the
present invention is a novel crystal which shows a X-ray powder
diffraction spectrum and a thermal decomposition temperature (Td) both
different from those of the well-known crystal of
2,3,6,7,10,11-hexahydroxytriphenylene monohydrate, and the crystal is
superior in thermal stability. Thus, since the type B' crystal and the
type C crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate
obtained by combining the production process of the present invention and
further the specified crystal precipitation process (crystallization
method) are superior in thermal stability, an equipment built-in with the
crystal of the present invention as a raw material of a functional
material has a superior stability (resistance to denaturalization) and
can maintain a desired performance over a long period of time.

INDUSTRIAL APPLICABILITY

[0074] The production process of the present invention allows an
industrial production and the like of hydroxytriphenylenes which are
useful as a raw material of functional materials such as, for example,
discotic liquid crystal and the like. In addition, since the novel
crystal of 2,3,6,7,10,11-hexahydroxytriphenylene monohydrate of the
present invention is superior in thermal stability, for example, when the
crystal is used as a raw material of a functional material for equipment,
the crystal allows a desired performance of the equipment to be
maintained for a long period of time.